Study: Marijuana-like substances in brain trigger appetite

Associated Press

Published Thursday, April 12, 2001

Scientists have found that marijuana-like substances naturally produced in the brain stimulate appetite -- a finding that not only offers clues to treating obesity but also explains why pot smokers get the ''munchies.''

The study suggests that these endocannabinoids are part of the brain's complex system for controlling when and how much to eat.

Scientists have known for several years about the existence of these substances, which are chemically similar to the active ingredient in marijuana but do not make people high.

However, their exact role in the brain was unclear.

In a study in Thursday's issue of the journal Nature, researchers found that mice that had been genetically altered so they could not respond to endocannabinoids ate less than normal mice did. The mice lacked ''receptor'' structures that endocannabinoids activate in the brain.

And when ordinary mice were given a substance that blocked endocannabinoids from acting at these receptors, they ate less than normal as well.

The findings help explain why marijuana users get a ravenous hunger -- the ''munchies'' -- after smoking pot.

''We know that the marijuana that gets absorbed activates these receptors, and now we show that activation of these receptors is involved in the increase of appetite,'' said Dr. George Kunos, who led the study as scientific director of the National Institute on Alcohol Abuse and Alcoholism at the National Institutes of Health. ''It was assumed that was probably correct. This just provides the evidence.''

Moreover, Kunos said, the study also suggests that endocannabinoids are part of the complex neural circuitry controlled by leptin, a hormone that tells the brain when it is time to lose weight. Already, leptin is known to reduce levels of several other appetite-enhancing substances.

It is unknown how endocannabinoids are created by the body, or precisely how they work. But the study found they can operate independently of the level of certain other appetite-triggering substances.

That suggests it is unlikely that efforts to control weight gain or loss with any single drug will be effective, Kunos said.